{-# LANGUAGE TemplateHaskell, TypeFamilies #-} module T10306 where import Language.Haskell.TH import GHC.TypeLits -- Attempting to reify a built-in type family like (+) previously -- caused a crash, because it has no equations $(do x <- reify ''(+) case x of FamilyI (ClosedTypeFamilyD _ _ _ []) _ -> return [] _ -> error $ show x )